In several diesel engines today, fluid control valves regulate the flow of actuation fluid to hydraulically actuated devices, such as hydraulically actuated fuel injectors and hydraulically actuated gas exchange valves, such as engine compression release brakes. Depending on the positioning of a valve member, the fluid control valve either connects the hydraulic device to a source of high pressure actuation fluid causing the device to activate, or connects the hydraulic device to a low pressure actuation reservoir causing the device to deactivate, reset itself, or remain inactive. Typically, the movement of the valve member is controlled by a solenoid actuator. For instance, hydraulically actuated fuel injectors such as that shown in U.S. Pat. No. 5,738,075 issued to Chen et al. on Apr. 14, 1998, include a solenoid driven fluid control valve that is attached to an injector body.
While the method of using a solenoid actuator to control a fluid control valve has performed well, there is room for improvement. For instance, the solenoid actuator includes a solenoid coil mounted to a stator. In some actuators, the stator is comprised of a relatively soft, magnetic material that aids in conducting the magnetic flux creating the energized solenoid coil. The stator defines a guide bore in which a push pin, which is operably coupled to the valve member, moves between a first and a second position. Because an outer surface of the moveable push pin makes contact with the inner surface of the stator, the movement of the push pin within the guide bore causes the relatively soft, magnetic material of the stator to wear. Over time, the rubbing of the relatively hard, nonmagnetic push pin against the relatively soft, magnetic stator decreases the durability of the solenoid actuator. Further, the relatively soft, magnetic material comprising the stator is worn by debris trapped between the outer surface of the moving push pin and the inner surface of the stator. This wear on the stator also decreases the durability of the solenoid actuator.
In addition to the rubbing between the outer surface of the push pin and the inner surface of the stator, there may be undesirable contact between the valve body and the moving valve member. The magnetic flux created by the energized solenoid coil is often asymmetrical, causing the push pin to misalign within the guide bore. The asymmetrical magnetic flux can cause the misalignment of the valve member and undesirable side forces if the valve member is attached to the push pin. A misaligned valve member can rub against the valve body causing the valve member and the valve body to wear and reduce its actuation speed.
The present invention is directed to overcoming one or more of the problems as set forth above.